In a typical cloud data center environment, there is a large collection of interconnected servers that provide computing and/or storage capacity to run various applications. For example, a data center may comprise a facility that hosts applications and services for subscribers, i.e., customers of the data center. The data center may, for example, host all of the infrastructure equipment, such as networking and storage systems, redundant power supplies, and environmental controls. In a typical data center, clusters of storage systems and application servers are interconnected via high-speed switch fabric provided by one or more tiers of physical network switches and routers, e.g., a Clos network. More sophisticated data centers provide infrastructure spread throughout the world with subscriber support equipment located in various physical hosting facilities.
In general, multicast service involves delivering data through a network to a group of subscribers, e.g., customers of a data center or servers within a data center, substantially simultaneously in a single transmission from a source device, e.g., a server. As an example, when two or more subscribers are interested in receiving the same multicast data, each of the subscribers may request to join a multicast group associated with the multicast data. The multicast data from the source is replicated, as needed, by physical network switches and routers within the network in order to reach the subscribers of the multicast group. The network switches and routers used to replicate and forward the multicast data for the multicast group may create a multicast distribution tree through the network for delivery of the multicast data.
In a case where a large number of servers are interconnected by a switch fabric, each pair of servers may have a large number of equal cost paths between them. In this scenario, layer two (L2) connectivity between the physical servers may become unmanageable, and the physical servers may only be connected to each other using layer three (L3) connectivity. The physical servers connected via the switch fabric may communicate using unicast service, but multicast service between the physical servers may be more difficult to manage due to the large number of redundant paths in the network. In some cases, a virtual overlay network may be built on top of the switch fabric to emulate an L2 network between virtual switches executed on the servers using a tunnel encapsulation protocol, e.g., IP-in-IP, NvGRE, or VXLAN. In order for the virtual overlay network to emulate L2 multicast service, however, the underlying switch fabric must also support multicast service.